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4EAT intermittent issue


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12 replies to this topic

#1 bridorf

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Posted 16 August 2007 - 07:18 PM

Just got back from a long trip to the Washington coast and while we were there the transmission did a strange thing - very intermittent so far - it has only happened twice.

*It happened once after a long drive and once when the car had only been driven approx. 8 miles. When cruising through town at around 35MPH the trans. seems like it can't make up its mind about what gear to be in for a second and feels like it disengages and then abruptly engages again. I have never felt anything like it before and can't quite explain it exactly, but it is really disconcerting and makes it hard to trust the car when it is so intermittent. We got back last night and the trip home was uneventful, but that was primarily at highway speeds. Again it only happened a couple of times and then the rest of the drive is uneventful. The fluid was changed recently and the color and level are good. And possibly there is nothing to be done until it fails or is problematic more consistently.

I am hoping that someone can enlighten me or this will be obvious to someone - i.e. bad computer, TPS adjustment, etc...

also - tires are new and pressures good, no codes in either TCU or ECU

#2 porcupine73

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Posted 16 August 2007 - 07:32 PM

Could be backlash in the system/lockup solenoid activating and deactivating. There is a note about this behavior for the phase II 4EAT (though that's not the AT you have).

tires are new

Is this an AWD vehicle and did this behavior start right after the new tires? Even if not all tires circumference should be measured with a narrow tape measure to be certain they are all within 1/4". Even brand new tires can have differences in circumference.

#3 Manarius

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Posted 16 August 2007 - 07:38 PM

My car - when the MAF first started going bad - did something rather similar to what you described. It just felt like a minor...burp in the system if you will. It would be driving along and a quick jerk and back to normal again.

#4 ericem

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Posted 16 August 2007 - 10:16 PM

I had that issue when I needed new wires and plugs.

#5 bulwnkl

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Posted 16 August 2007 - 10:38 PM

I had this issue once on a 1990 with an A/T. It turned out to be the TPS. OTOH, that was a Dodge Shadow... :P

#6 bridorf

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Posted 16 August 2007 - 11:22 PM

I recently have replaced the steering rack, right front wheel bearing, plug wires, knock sensor, trans. fluid change and injection relay. I also used some BMW synth. 15W50 motor oil from work that was free (seems a bit heavy for this motor, but it is a warm summer). Obviously if the issue was consistent I could put a few of the old items I just replaced and try to rule out some change I made. Could any of these items make a difference in TPS behavior? I have also noted a slight whistling sound from somewhere, air past throttle plate?, at very light throttle - possibly an indication it needs some cleaning and adjustment checking.

I dealt with the torque bind thing a couple of years ago and after transfer housing removel and solenoid & clutch pack replacement - the issue was due to a bad TCU. The used one I put in is an exact match for the one that came out - but I am somewhat suspect of that too.

I've also been reading about this front pump in the 4EAT - I do have a whine from the trans. that I could never hear over the wheel bearing and the wind noise from the missing, but now replaced, plastic covers for the side view mirrors. Any chance this is the culprit, and what is involved in repairing it?

#7 bridorf

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Posted 17 August 2007 - 01:42 PM

bump

#8 porcupine73

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Posted 17 August 2007 - 01:54 PM

Whistling sounds can also be dirty IACV. What speed(s) do you hear the whine?

Does the AT feel like this? (It's for 4EAT Phase II but I've noticed similar behavior in the phase I's)
2. Shock felt during light acceleration with the Lockup clutch applied.

Symptom When the driver tries to lightly accelerate the vehicle, when driving at a constant speed in 4th gear and the Lockup clutch is engaged, they may feel a slight shock through the body of the vehicle. Some customers may compare it to a Manual Transmission vehicle.

Mechanism When the accelerator is pressed lightly (approximately 20% or less), the lockup clutch is not released. This causes a direct coupling between the engine and the drive train of the vehicle. The slight shock is from the small clearances in the drive train gears, axle splines, etc. If the lockup clutch is not applied then, the shock is absorbed by the fluid coupling in the torque converter. Under certain conditions, this same shock can also be felt when activating the cruise control.

Recommendation Explain to the customer what they are feeling is a normal operation. Basically, the lockup clutch is kept on as much as possible to increase fuel economy of the vehicle. Increasing the engine load (driving on hills or pushing the accelerator more) will disengage the lockup clutch sooner.

We recommend you try duplicating this during some of your road testing (PDI) so you are familiar with the sensation. To do this, drive at a constant speed around 40 mph. Confirm that the lockup clutch is applied (use Select Monitor) and accelerate using light throttle. You will feel a slight shock throughout the body of the vehicle.

#9 bridorf

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Posted 17 August 2007 - 10:05 PM

What is the IACV?

and I notice the whine when cruising on highway light to no load on motor - as soon as I put my foot into the pedal slightly the whine goes away - didn't really concern me until I read about the front pump issue. It wouldn't suprise me to have a trans. with 190,000 on it to make some noise.

The AT shift problem doesn't feel like that which you described - at least I don't think so. My wife has been driving the car the past two days in all sorts of driving situation without any issue at all. Could a TPS issue be so intermittent?

#10 porcupine73

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Posted 18 August 2007 - 06:45 AM

Did the transmission issue start after the new tires were installed?

IACV is idle air control valve. Subaru sometimes calls it ISC idle speed control valve. There is an article here on endwrench about cleaning it, but it is for the phase II style which has the IACV intake on the top of the intake manifold (which is not what you have).

In this pic, the IACV is right above the circle for the ECTS, right below the hose coming off the PCV valve.
Posted Image

#11 bridorf

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Posted 26 August 2007 - 06:37 PM

The whine is definately coming from the transmission area - could just be normal front gearbox noise - not very perseptible.

The transmission issue did start after the tires were replaced, but a few months after. I had recently replaced the knock sensor, steering rack, and had a alignment performed prior. I don't see anything amiss anywhere, and I've changed the trans. oil which looked good and is at the proper level. Just every once in awhile the car will hiccup and it is definately a transmission thing - I just have no idea what it could be and was hoping for some possible insight or if anyone had experience with a similar issue. Or I'll just wait for it to happen more often or fail...

#12 x_25

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Posted 27 August 2007 - 09:57 AM

I can't give any advice on how to fix it but i can tell you that the 4EAT in my '99 Outback whines, but it is very quiet and can only be heard with the radio off. That is the way it has always been. Last winter when i was driving the car it hiccuped just like you described, it seemed to for no reason on a flat stretch of road with no gas peddle input decided to shift from third to second back to third. It has only ever done it once so i dont see it as that big of a deal with my car. The car has 130k miles on it now.

#13 bridorf

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Posted 29 August 2007 - 11:21 PM

Just an update:

Today my wife said the CEL came on and the car ran a bit rough - finally a problem that presents itself properly. - I pulled a code #42 for the idle switch and visited the TPS - all looks good - unplugged connection and plugged it back in - cleared code and car ran fine and did not reset code in the 15 miles I drove it.

Could this TPS fault code be related to my strange trans. problems, and what does this fault code generally mean?




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